This invention relates to devices for sensing the relative proportion of a gas in a mixture of gasses. The new gas sensor device may compare a known gas or gas mixture to a varying or fluctuating gas mixture for use in measuring the amount of a particular gas in the varying mixture.
Devices currently exist for use in sensing the amount of a gas in a continuously flowing gas mixture. As an example, for underwater human divers it may be important to know the amount of helium in a breathing mixture being supplied to the diver from gas tanks. A device that includes a temperature sensitive coil of wire suspended in a chamber therein may be used to detect changes in the thermal conductivity of a gas mixture flowing through the chamber if the gas composition changes.
A detector wire coil in the gas flow through chamber may be compared to a reference wire coil in a separate chamber containing a gas mixture of a chosen mixture content. The electric current difference between the two wire coils may be measured as for example by use of a Wheatstone bridge. The percent variation based on the varying conductivity with temperature of the wire coil may be used to calculate the amount of helium in the gas flow mixture. This type of device may also be used to detect other gas percentages as well. For example, hydrogen content may be similarly measured when mixed with nitrogen, oxygen or air.
The difficulty in using such devices in an underwater diving environment or other limited control measuring environment may be the need to provide a relative uniform gas mixture flow rate through the detector wire coil chamber for comparison to the reference wire coil. To the extent this is not well controlled the temperature change at the detector wire coil may not be principally due to the helium, hydrogen or other gas mixture changes and therefore the comparison measurement may be inaccurate. Also the suspension of the wire coil in the chamber may cause problems due to the vulnerability of the wire to the gas flow environment and other factors such as impact to the device.
The present invention is directed to apparatus for sensing a proportion of a gas in a gas mixture. A gas sensor may have a sampling element slidably engaged with a sensor element. The sensor element may have a sensing chamber therein with an inlet passage and an outlet passage formed in the sensor element wherein the inlet passage and the outlet passage may be in communication with the sensing chamber and externally to the sensor element. A first detector may be positioned in the sensing chamber with a first pair of external contacts passing through the sensor element terminating externally thereto. The sensor element may have a reference chamber therein with a second detector positioned therein and a second pair of external contacts passing through the sensor element terminating externally thereto. The sampling element may have a sample chamber therein with the sensor element forming a portion of the sample chamber. There may be a gas inlet port in the sampling element that may be in communication with the sample chamber and externally to the sample element.
These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.